Interesting twist: I have State Farm for everything, house, cars, life, etc. Plus I have a fairly decent umbrella liability policy with them.
I originally insured the Firebird with SF when I bought it because it was quick and easy, thinking i'd figure out the best carrier later.
Well it turns out that if I want to go with Hagerty, or someone else for the bird (or any other car), my premium for the umbrella policy would go up by $500/yr. As the agent explained, if there is potentially another insurance co involved in an umbrella liability claim then it's more expensive for SF to coordinate with other lawyers, etc. Which I guess makes sense.
That said, they are charging me $225/yr for $30k agreed value. Grilled my agent extensively on the terms (per all the Hagerty discussions) and I was satisfied. Hagerty was about $400 iirc.
